For modern and future communication networks including mobile/wireless communication networks (such as for example General Packet Radio Service (GPRS), Universal Mobile Telecommunication System (UMTS), Long-Term Evolution (LTE), Long-Term Evolution Advance (LTE-A), or other 3GPP (3GPP: Third Generation Partnership Project) networks, or the like), there is known a concept of a simultaneous presence of home and macro network access.
Accordingly, the following specification relates to mobile wireless communications, such as 3GPP UMTS, Long-Term Evolution (LTE & LTE-A) or the like, and is related more specifically to an interworking of a home nodeB or the like and networks comprised of macro nodeBs or the like.
For the subsequent specification and the terminology used therein, the following is to be noted. The term “HNB” is a terminology commonly used for WCDMA/HSPA (WCDMA: Wideband Code Division Multiple Access, HSPA: High Speed Packet Access) home equipment. For LTE and LTE-A the term commonly used for home equipment is “HeNB”, where the e stands for evolved. The macro nodeB for UMTS is commonly called “nodeB” (“NB”), whereas for LTE and LTE-A the macro nodeB is commonly called “eNB”, where the e stands for evolved. The subsequent text uses the terms home nodeB or “HNB” and macro nodeB or “MNB” as non-limiting examples only, without limiting the thus described techniques and concepts to any one of UMTS, WCDMA and/or HSPA. Rather, the thus described techniques and concepts may equally be applied in other systems as well, such as for example LTE and LTE-A.
Furthermore, it is to be noted that any home equipment may comprise several techniques to serve different end user equipment within a CSG (closed subscriber group), thus a home cell or femtocell may be formed of a combination of a HNB and a HeNB.
FIG. 1 shows, in two alternative illustrations, a schematic diagram of an architecture of a simultaneous presence of a home cell and a macro cell, in which exemplary embodiments of the present invention are applicable.
As depicted in FIG. 1A, a mobile station or user equipment UE may be connectable both to a home access network denoted as home cell and/or a macro access network denoted as macro cell. Typically, while access to the home cell is restricted for a closed subscriber group (CSG) being authorized for the respective home cell, access to the macro cell is commonly available. Stated in other words, the home cell may be a private access facility, while the macro cell may be a public access facility such as a 3G radio access network (RAN). In 3GPP, a home cell is also referred to as femtocell.
As depicted in FIG. 1B, a mobile station or user equipment UE may be connectable to a backbone or core network via a home cell or access network (AN) or via a macro cell or radio access network (AN). An exemplary home cell according to FIG. 1B comprises a home base station or home nodeB (HNB), to which the UE is connectable, for example by a wireless link, and a respective home base station or home nodeB gateway (HNB). The HNB aggregates traffic from a large number of HNBs, although this is not depicted in FIG. 1B for the sake of clarity. An exemplary macro cell according to FIG. 1B comprises one or more macro base stations or macro nodeBs (MNB), to which the UE is connectable, for example by a wireless link, and a radio network controller (RNC) or the like.
Home cells, i.e. home nodeBs, are intended to enhance the coverage of a public radio access network such as a UMTS RAN in a home environment, such as for example a home or apartment, i.e. a private location. Accordingly, home cells, i.e. home nodeBs, provide radio coverage for mobile stations or user equipments within a home environment in addition to radio coverage provided by macro cells, i.e. macro nodeBs. Traffic of/in home cells may thus bypass the mobile infrastructure of mobile network providers such as a UMTS RAN. A deployment of home cells or home nodeBs in parallel to a deployment of macro cells or macro nodeBs is not controllable. Therefore, with increase in the number of deployed home cells or home nodeBs within an overall macro network deployment, there arise problems of interference there-between.
Namely, the simultaneous presence of a home nodeB (HNB) and a macro nodeB (MNB), sharing the same part of the radio spectrum, may cause severe interference scenarios. A user equipment UE being allocated to a macro cell, which receives macro cell signals with a power close to a service-specific power set threshold, may be desensitized by the HNB transmit power. This is because of the problem that that the HNB power received is too large so as to properly receive and decode a MNB signal.
As mentioned above, a HNB is only accessible for the set of users assigned to the closed user group (CSG) of the HNB. Thus, no handover from the MNB to the HNB is possible for the user equipment for getting out of the above-outlined interference scenario. Otherwise, macro cell activities to improve the wireless link to the user equipment will cause capacity losses in the macro cell and will increase interference to the home cell.
In view of the above problem, there is a need for enhanced interference management techniques in a home network environment so as to mitigate interference between home and macro cells.
In this regard, there has been proposed a technique considering that the user equipment may report the HNB interference situation and the macro cell may utilize the backbone/core network to reduce the transmit power of the HNB so as to reduce the interference from the home cell to the macro cell.
The thus proposed technique is explained with reference to FIG. 2. FIG. 2 shows, in two alternative illustrations, a schematic diagram of an operational principle of a known interference mitigation technique in a home environment.
As depicted in FIG. 2A, a user equipment UE, which is authorized for the macro cell, but is not authorized for the home cell (i.e. does not belong to the CSG of the home cell), may be camping in the macro cell in vicinity of the home cell's coverage area. Hence, the UE camping on the macro cell may identify an interference being caused in the macro cell by the transmit power of the home cell, i.e. the HNB of the home cell, and may report the presence of this interference to the macro cell, i.e. the MNB of the macro cell. The macro cell, i.e. the responsible MNB, may address, via the HNB gateway, the HNB causing the interference for sending power down commands (power reduction commands) until the user equipment UE camping on the macro cell stops the interference reporting, namely until the interference is removed due to sufficient transmit power reductions at the HNB. The power down commands are proposed to be relative values, e.g. 2 dB step down.
While the above-outlined technique is practicable in a scenario of one macro cell related to one HNB and one UE affected by interference, it is not practicable is more difficult scenarios, for example when several UEs and/or macro cells (and one home cell) are involved.
Such a more difficult scenario is depicted in FIG. 2B. As depicted in FIG. 2B, there is exemplarily assumed a scenario with three UEs, all of them being not authorized to camp on the home cell, and these UEs are allocated to three different macro cells. All of these UEs have a high interference impact by a single HNB. All MNBs will receive interference reports from the respective UE in its macro cell, and consequently they will initiate, via the HNB gateway, the sending of power down commands (power reduction commands) to the same HNB of the relevant home cell. This may lead to an execution of more power down operation at the HNB than necessary, and may lead to an extinction of the home cell, i.e. a shrinkage of the home cell's coverage (close) to zero, practically providing no coverage to the CSG users any more.
There is no possibility of avoiding such a problematic outcome. In particular, it is neither applicable nor practicable to provide countermeasures at the HNB gateway. This is because such a HNB gateway is typically controlling many thousands of HNBs, and it would lead to huge management functions to control at the HNB GW how far more than one macro cell may try to address the same HNB at the same time.
Accordingly, in view of the above, there is a need for enhanced interference management techniques in a home network environment so as to mitigate interference between home and macro cells, which may avoid excessive degradation or even extinction of a home cell causing interference in a macro cell.